Safety electric mine lamp



J y 4, 1939- w. K. WILBUR ET AL 2,165,193

SAFETY ELECTRIC MINE LAMP,

Original Filed July 15, 1955 a at Imvenfira Z0 v1 fl'wwr m Garage 0.11 1 2%,

Patented July 4, 1939 UNITED STATES PATENT OFFICE SAFETY ELECTRIC MINE LAMP Application July 15, 1935, Serial No. 31,488 Renewed October 8, 1938 15 Claims.

This invention relates to improvements in mine lamps and is particularly concerned with a cheap, light, simple and safe construction of such devices.

Certain governmental regulations control the acceptability of mine lamps which are to be employed in mines in which there is danger of gas or like explosions by reason of the exposure of sparks or flame to the atmosphere in such mines.

It, therefore, has been proposed to safeguard such lamps by providing electric bulbs which are enclosed within flame-tight structures so that short circuit sparks cannot communicate combustion to the dangerous gases. It has likewise been is proposed to support an incandescent light bulb in such a manner that a cracking of the bulb is immediately accompanied by the physical disruption of the same under conditions to cause extinction of the filament and thus prevent explosion. Devices have also been proposed for employment in this way in which the bulb is broken and ejected from its contacts upon fracture.

According to the present invention, a very simple and light construction is aiforded by the omission of an external gas-tight or flame-tight enclosure for the bulb, and by providing safety devices for breaking the bulb upon fracture of the same and thereby effecting an interruption of 1 the circuit so that short circuit sparks are not produced. Other phases of the present invention have to do with the manner of mounting the bulb and its protective elements and in establishing electrical connection thereto.

35 A particular feature of the present invention is the employment of an electric light bulb of particular type, having incorporated therein a reflective surface which controls and directs the illumination from the filament and produces the 40 governmentally demanded conical angle of illumination, and without the necessity of providing safety devices or other structures which obstruct or locally obscure the illumination afforded.

In conjunction with the employment of a light bulb having a self-contained reflector surface, it is preferred to have this surface deposited externally on certain portions of the bulb, and to employ a conductive material for this reflector and to establish a. current path through the safety devices and through such reflective coating as a means of delivering the current to or from the filament.

with these and other features as objects in view,

an illustrative form of practicing the invention is shown in the accompanying drawing, in which:

Figure l is a side elevation of the mine lamp structure on a large scale;

Fig. 2 is a sectional view diametrically through the axis of the holder;

Fig. 3 is an end view of the lamp. 5

In the drawing, the lamp bulb B is shown to have a base member Ill with the usual locating and holding pins H as employed in automobile bulbs, for example. Such pins cooperate with slots in a holder, and the assembly is commonly in known as a Swan connection. The bulb also includes a transparent glass portion l2 which, in the present illustration, is at the top or axis of the bulb and forms a dome of relatively thick glass. The flanks l3 of the bulb are of relatively l6 thinner glass, and are covered by a frangible reflective coating H of deposited metal. The provision of such coating is old and well known in the art, and does not by itself form a part of the present invention. It is preferred to have the 20 reflective coating extend slightly above the greatest diameter of the bulb and beyond the filament F, so that the conical angle of illumination from such a bulb is substantially that demanded by governmental regulation, which presently is 130.

In the preferred form of construction, as illustrated, the coating 14 is carried down to the external metal portion of the base member so that there is electrically conductive relation of these parts.

The base member it) includes the usual internal structures for supporting the central contact l5.

This bulb is fixedly held in position on the insulating member 20 which is illustrated in the 5 form of a cup with bayonet slots H for receiving the pins ll of the bulb in the usual way. The base of the cup 20 is provided with a resilient contact 22 for engaging the central contact l5 of the bulb.

A metal sleeve 25 surrounds the cup 20 and has the crimped portions 25a, 25b for maintaining it fixedly in position. The surface of this sleeve 25 may be rolled to form a thread 26. Extending upwardly from the sleeve 25 are aplurality of fingers 21 which rest against the bulb at the coated portion thereof, so that shadows are not cast by these fingers 21. This also brings the ends of these fingers into engagement with the bulb at the thinnest glass section thereof. It is preferred to so dispose the fingers with relation to the location of the bayonet slots 2| that the fingers (Fig. 3) move relatively in planes parallel to the plane of the filament, in such a way that the fingers do not come in contact with the filament when these fingers move inward as a result of the crushing of the bulb. The fingers are resilient and press inward with a force which is insuflicient to cause fracture of a sound bulb, but sufiicient to produce crushing of a bulb in which the arch-like continuity has been interrupted by the fracture of s'ufi'icient extent to render the bulb unsafe for employment under the conditions specified above. Each of the two illustrated fingers constitutes a reaction means for the other, to avoid unilateral stressing of the bulb and holder.

The sleeve 25 is received tightly in a shield and supporting member 30 (Fig. 1) which includes a visor or guard-piece 3| extending above the bulb to protect it against rock or the like falling from above. The support member 30 also is provided internally with a threaded portion 32 for cooperatiori with the threads 26 in holding the structure assembled. A cable connection 33 passes through a side wall of the support member 30 and has its terminals (Fig. 3) joined to the sleeve 25 and to the resilient contact 22. This support member also includes a blade 34 (preferably of aluminum for stiffness and lightness) for engagement with the loop of the miners cap.

It will be seen that the structure is small and compact, affords the required angle of illumination and is without loss by absorption through a screen or lens, and by its lightness and small dimensions is excellently adapted for the usual wearing on a miners cap.

If a falling rock, or a fragment projected by a tool or by explosion, should come in contact with the fragile portions of the bulb, a fracture or breakage results. If this fracture be of major extent, the fingers 21 immediately operate to break and crush in the side walls of this fragile portion and thus destroy the bulb and its reflective surface and demolish this portion of the current path so that the fragments fall free and the current is interrupted and there no longer exists a current path from fingers 21 to the filament. The rupture of the vacuum within the bulb assists in this operation, and it has been found in practice that the filament will be cooled and ex tinguished before a combustible gas can be ignited thereby. Furthermore, this current path cannot be restored by moving the fingers, but a new bulb must be inserted in position to accomplish this.

A particular feature of the construction is the provision of insulation in the holder whereby a current path is not established directly to or from external metal parts such as the blade 34 with respect to the filament and conductors in the cable connection 33. In the illustrated form, in particular, this is attained by having the threaded portion 32 of insulating material and extending around and protecting all parts of the sleeve 25 and preventing any normal contact with this sleeve and its fingers 2'1, and likewise extending across the end of the device to protect the ends of the conductors where they are joined to the central contact 22 and to the sleeve 25. In this way the guardpiece 3| and the blade 34, if of conductive material, are not charged with current from the lamp battery; and, on the other hand, current is not conducted therethrough to the conductors in cable connection 33 so that an accidental contact of such metallic structure with a trolley wire is prevented, within the lamp structure, from establishing any circuit, possibly through the wearers person, to the ground.

It is obvious that the invention may be employed in many other ways within the scope of the appended claims.

Having thus described the invention, what we claim as new and desire to secure by Letters Patent, is

1. A safety electric mine lamp comprising an exposed electric light bulb having a base member and a light-transmitting bulb portion having a thick end section and a thinner section adjacent the maximum diamter; a holder including means engaged with said base member for holding said bulb fixedly against withdrawal movement along the axis of said base member and a guard extending above the bulb, and safety circuit breaking means including a resiliently pressed finger located between the bulb and guard and pressing against said bulb at a point at the thinner section thereof for crushing the bulb portion when cracked.

2. A safety electric mine lamp comprising an electric light bulb having a base member, frangible conductive reflector means closely surrounding said bulb and extending substantially from the base member to points opposite the filament cf the bulb and connected electrically to the filament, a holder including means engaged with the base member for holding said bulb fixedly against withdrawal movement along the axis of said base member, and safety circuit breaking means including a resiliently pressed conductive finger bearing against the reflector for exerting stress upon said bulb, said finger being located in the shadow of said reflector so that it does not extend into the path of useful rays from the filament and reflector and operating when the bulb is cracked to demolish the bulb and reflector and interrupt the current path to the filament.

3. A safety electric mine lamp comprising an electric light bulb having a conductive coating constituting a reflective surface over a part of the bulb area and a conductive connection from said coating to the filament, means for holding the bulb, safety circuit breaking means including a resiliently pressed finger engaged with said coating and providing therewith a path for current to the filament and operating to demolish the conductive coating and thereby interrupt the current path upon fracture of the bulb, and reaction means engaged with another part of said coating.

4. A safety electric mine lamp comprising an electric light bulb having a conductive coating constituting a reflective surface over a part of the bulb area, and a conductive connection from said coating to the filament, means for holding the bulb, safety circuit breaking means including a plurality of opposed resiliently pressed fingers engaged with said coating adjacent the maximum diameter of the bulb for moving inward upon cracking or breaking of the bulb and thereby demolishing said bulb and conductive coating, at leastone of said fingers having a conductive portion cooperating with the coating in providing a path for current to the filament, said path being interrupted upon demolition of said-coating.

5. A safety electric mine lamp comprising an exposed electric light bulb having a glass portion and a base member and being substantially symmetrical about an axis passing through said portion and member, the glass portion being thicker at the intersection with said axis than at the sides and having a reflective conducting coating thereon in conductive relation with the bulb fila-- ment, means for holding the bulb against axial movement, and safety circuit breaking means including a resiliently pressed conductive finger engaged with the coating at the thinner part of said glass portion and operating when the bulb is cracked to demolish the bulb and coating and thereby interrupt the flow of current to the filament.

6. A safety electric mine lamp comprising an electric light bulb having a base member with locating pins thereon and a conductive coating upon the bulb connected to the filament thereof, a hoiderincluding means for enga g said base member and pins for holding said bulb against withdrawal, safety circuit breaking means including a resiliently pressed'metal finger bearing against said coating and bulb at a point substantially at the maximum and providing with said coating a necessary part of the current path of flow to the filament, said holder including insulation connected to said finger for maintaining the same insulated with respect to the base member of the bulb.

7. A safety electric mine lamp comprising an electric light bulb having an insulating lighttransmitting portion and a conductive reflectin coating extending over a part of said light-transmitting portion, a filament in said bulb and means providing a current path to and from said filament, said path including said coating as a necessary part thereof; a bulb holder; and conductor means connected with said holder and associated with said path-providing means and including conductive portions engaged with the coating at a portion thereof located on said lighttransmitting part of the bulb.

8. A safety electric mine lamp comprising an electric lamp bulb having a base including first conductive elements, a light-transmitting portion and a conductive reflecting coating, a filament, and means including said coating and conductive elements for providing a current path to and from said filament; and a supporting and protecting structure for said bulb including a holder engaged with said base, second conductive elements insulated from said base and engaging said coating, a guard piece extending over the conductive portion of the bulb and over said second conductive elements and an attachment member, the portions of said supporting and protecting structure which comprise said guard piece and attachment member including exposed metal pieces, and insulation in said supporting structure for interrupting electric conduction from said metal pieces to said path.

9. A safety electric mine lamp comprising an electric light bulb having a frangible conductive coating constituting a reflective surface over a part of the bulb area and conductively connected to the bulb filament, means for holding the bulb, and a plurality of resiliently pressed conductive fingers engaged with said coating adjacent the maximum diameter of the bulb at a plurality of points around the periphery of the bulb and providing with the coating a necessary part of the path for flow of current to the filament, said fingers engaging said coating with insufiicient pressure to break a sound bulb and operating upon cracking of the bulb to demolish the same and said coating and thereby interrupt the fiow of current to the filament.

10. A safety electric mine lamp comprising an electric light bulb having a conductive coating constituting a reflective surface over a part of the bulb area and a conductive connection from said coating to the filament, means for holding the bulb, and safety circuit breaking means indiameter of the bulb eluding a resiliently pressed conductive finger engaged with said coating, and reaction means enaged with a part of said coating substantially diametrically opposite the point of engagement of said finger therewith, said coating and finger constituting an essential part of the current path for energizing the bulb, said finger operating when the bulb is cracked to demolish the bulb and coating and interrupt said energizing current path to the filament.

11. A safety electric mine lamp comprising an electric light bulb having a base member, a bulb portion, a frangible conductive coating on a part of the bulb portion, and a filament conductively connected to said coating, a holder including means engaged with said base memer for holding said bulb against withdrawal from the holder, 2. resiliently pressed finger supported by the holder and bearing against said coating and said bulb substantially at the maximum latter for crushing the same when cracked, means included in the bulb and holder for providing in conjunction with said finger and coating the sole conductive path for current to the filament, and a guard connected to said holder and having an attachment piece and a protector member located over the bulb and finger when said attachment piece is in position on a cap support, said finger operating in crushing the bulb to disrupt the said conductive coating and interrupt the circuit to the filament.

12. A safety electric mine lamp comprising an electric lamp having a base member, a bulb and a frangible reflective coating extending over a portion of the bulb from said base member and terminating at a radial plane through the lamp axis substantially at the maximum diameter of said bulb, a holder including means for holding said bulb fixedly against withdrawal movement along the axis of said member, and safety circuit breaking means including a resilient finger mounted on the holder and pressed against said coating at a point adjacent the edge of said coating, said finger being located wholly within the shadow of said coating so that a conical beam of substantially uniform character is projected through the uncoated portion of the bulb.

13. A safety electric mine lamp comprising an electric lamp having a base member, a transparent glass bulb, a filament and a fragile conductive coating constituting a reflective surface over a part of the bulb area and electrically connected to the filament, another part of the bulb area being free of the coating for permitting the outward passage of light; a holder including means for holding said base member against removal from said holder; a resiliently pressed conductive finger supported by said holder and bearing in conductive relation against said coating at a point adjacent the edge of the coating with the finger located wholly in the shadow of said coating; and circuit means including said finger and coating in series as a necessary part thereof for current flow therethrough to the filament so that rupture of the bulb and itscoating will interrupt the flow of current to the filament.

14. A safety electric mine lamp comprising a bulb, a filament therein, a base member for said bulb, means for establishing a circuit through the filament including a frangible conductor, a resilient member rigidly supported by said base member and bearing against the bulb, said resilient member being tensioned and so associated with the bulb and said frangible conductor that the weakening of the bulb at any point therein diameter of the will result in the destruction of the bulb and a mechanical destruction of the frangible conductor.

15. A safety electric mine lamp comprising a bulb, a. filament therein connected to one electric supply terminal, a base member for said bulb, a conductive resilient member rigidly supported by said base member and bearing against the bulb and connected to the other electric supply terminal, a frangible conductor establishing a circuit from said resilient member to the filament, said resilient member being tensioned and so associated with the bulb and frangible conductor that the weakening of the bulb at any point therein will result in the destruction of the bulb and a. mechanical destruction of the frangible conductor.

WILLIAM KNAPP WILBUR.

GEORGE C. N'ELMS. 

